Switching



H. B. MARTIIN SWITCHING Filed April 19, 1934 INVENTOR H MARTIN- MTII'ORN IEW Patented Apr. 7, 1936 UNITED STATES PATENT oFFicE 2,036,712 SWITCHING" of Delaware Application April 19, 1934, Serial No. 721,254

3 Claims.

My present invention relates to a multi-range oscillation generator.

An oscillation generator of considerable utility is one wherein the plate of a tube is connected to one end of the coil of a tuned circuit, the filament or cathode of the tube to some intermediate point on the coil, and the grid of the tube connected to the other end of the coil.

Heretofore, large frequency changes have been accomplished with this arrangement by shunting in and out of the circuit a portion of the coil adjacent the plate or anode. Such a frequency changing arrangement, however, is objectionable inasmuch as the cutting in and out of this portion of the tank coil results in improper grid excitation, necessitating additional adjustment of the grid or filament connection or both.

To avoid the foregoing difliculty is the main object of my present invention and I carry it into effect by cutting in and out a portion of the tank coil lying on both sides of the cathode tapping point. In a way which shall be more fully described hereinafter, this simultaneous cutting in and out of this portion of the plate coil simultaneously adjusts the feedback coupling so that at all frequency ranges optimum values of grid excitation follow.

My present invention is described more fully with the aid of the accompanying drawing, wherein Figure 1 illustrates, in conventional manner, an oscillation generator whose frequency is changed in the way known to the prior art, and Figure 2 illustrates the manner in which frequency change-over is accomplished in accordance with the principles of my present invention.

Turning to Figure l, a vacuum tube or multielectrode discharge device 2 having an anode 4, a cathode 6, a grid 8, and a screen grid I0 is provided with a tunable tank circuit l2. The tank circuit l2 consists of a coil l4 and variable condenser H5. The cathode 6 is grounded, as illustrated, and is thereby effectively connected to point I8 on coil l4 which is effectively grounded for the oscillatory currents involved by means of lay-passing condenser 20. Grid bias is established by way of a grid leak resistor 22, and the plate 4 is coupled to the tank circuit I2 by way of radio frequency condenser 26.

In order to shift the operating point from a lower frequency to a higher frequency in the arrangement of Figure 1 which, as already indicated, is old and well known to the prior art, range switch 28 is closed, short-circuiting portion 30 of coil l4. However, it will be found that at the higher frequencies the grid is subject to inordinately high excitation and this, of course, necessitates the moving of tapping point l8 towards the lower end of coil l4.

This disadvantage is overcome according to my present invention which is illustrated in a diagrammatic and conventional form in Figure 2. Thus, turning directly to that figure, when the range switch 28 is closed, a portion of the tank coil on either side of tapping point I8 is shortcircuited, the portions AC and. BC on the coil being so chosen as to give the proper change in frequency with a simultaneous reduction in coupling to the grid so as to provide for optimum excitation conditions. Ordinarily, the section AC will be larger than the section BC short-circuited, although in certain instances it may be found that optimum working conditions will be had with AC equal to BC or possibly less than the latter.

A flexible copper braid 48 is connected between. the blades of range switch 28 and the tapping point or grounding point 18 in order to insure a ground radio frequency potential at points A and B instead of at some point intermediate points A and B.

To summarize, referring to Figure 2, when the portion A, B, C of the tank coil I 4 is short-circuited out, grid excitation is maintained constant or allowed to increase only slightly, depending on the choice of taps A, B and C. Ordinarily, oscillation generators of this type require a slight increase in grid excitation at the higher freiii) quency range, but not nearly as much as would occur if the old method shown in Figure 1 were used. Consequently, excitation for both ranges is maintained correct and the entire system becomes much more stable through both ranges, avoiding much of the heretofore experienced drifting tendencies, caused by over excitation in the higher frequency range.

While I have described my invention with particularity in connection with the accompanying drawing, it is to be clearly understood that it is not to be limited thereto, but is to be given the full breadth, depth and width of the appended claims.

Having thus described my invention what I claim is:

l. A variable range oscillation generator comprising a tube having an anode, a cathode, and a grid, a frequency determining circuit comprising a coil connected at one end to said anode, at an intermediate point to said cathode, and at its other end to said grid, and means for short-circuiting a portion of said coil about the point on said coil connected to said cathode.

2. Apparatus as claimed in the preceding claim, including a low resistance connection between said intermediate point and said shortcircuiting means for maintaining a predetermined point on said coil at substantially zero radio frequency potential when said short-circuiting means is efieotive to short-circuit a por-- tion of said coil.

3. A variable range oscillation generator comprising an electron discharge device having an anode, a cathode, and a grid, a frequency determining circuit comprising an inductance coil in parallel with a variable condenser, a connection including a condenser from one terminal of said circuit to said anode, a direct connection from the other terminal of said circuit to said grid,

a connection including a radio frequency by-pass condenser from a point intermediate the ends of said inductance to ground, a source of biasing potential connected to said point through a grid leak resistor, a pair of serially connected condensers between the legs of said cathode, a ground connection to the junction point of said pair of condensers, a blade switch for shunting out a portion of said inductance about said intermediate point which is connected to ground, and a flexible copper braid connected between said intermediate point and a blade of said switch for effecting substantially the same radio frequency potential on the points of said inductance connected to the switch as on said intermediate point.

HERSCHEL B. MARTIN. 

